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Exchange 2010 offsite DAG

I currently have a 2 server DAG internally in the office.  This is healthy and working.  I want to host a 3rd member offsite in another state so in the event that the office power is out, a disaster occurs, and so on, mail will continue to flow, users can access email via smart device, laptop, etc.  I'm sure this is a pretty general question, but how do I proceed??!!  I have access to a colo and I can setup a VPN between the 2 sites if need be.  Will I need a DC at the offsite location as well as Exchange?  I"m sure mail flow can be managed with MX records and I've come across some 3rd party apps that can act as an https redirector for OWA.
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The shortest is to read recommended approach, highly recommended.
Plan appropriately.
Yes you would need the ADC if you want to have DR setup
Adam BrownSenior Systems Admin
Top Expert 2010
Exchange doesn't function without a DC to talk to, so yes, you'll need another DC at the offsite location. You'll also want to make sure those servers are set up with their own Active Directory site so you can properly implement Datacenter Activation Coordination functionality. You'll want to go through this: https://technet.microsoft.com/en-us/library/dd979781(v=exchg.141).aspx

If you aren't aware of AD Sites and Services configuration, you'll want to read up on that (it's a more complicated subject that you'd think).

Ronin's response points you to an Exchange 2016 recommended solution, and while that will be helpful, there is enough different between 2010 and 2016 that you'll want to read the 2010 documentation instead.

Also, note that the Offsite location must always be connected to your primary site, so if you use a VPN link between them, make sure to use a Point to Point VPN instead of an on demand VPN.

Also, don't use HTTPS re-directors for redirecting clients. You should either use BGP routing or globally capably load balancers to redirect all traffic to the offsite or point DNS records to the secondary site's servers if a failover occurs. Re-directors will likely cause problems.
AmitIT Architect
Distinguished Expert 2017
You are looking for Active/Passive DR setup. Remember, DAG role just designed to give HA for Mailbox role. If you need HA for CAS, you need HLB. Hub is by default HA.

Next, there is no automatic failover of services. Only DB failovers. In case you have an issue at your primary site, you need to perform manual steps to move users to DR site. Like DNS change, DAG shrink etc.

Is that easy? No, it is complex and expensive setup, if you are not having large user base, then keep server on Primary site. OR you can look for Office 365, which comes with HA by default.

Finally, HA is not only starts with Exchange, you need to start from server power source/switch/router/server/disk/RAM/CPU etc. till end user.

Can I normal admin implement this? No, you need IT Architect for each technology to set this up for you.
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